It is most physiological for a woman to bear one baby. But there are also multiple pregnancies, in this case twins or triplets are born. This is not such a rare occurrence, for example, there are one twins for every 40 births. To understand why twins are born, you need to know, at least in general terms, how fertilization occurs.
About once a month, in the middle of the menstrual cycle, a healthy woman ovulates. A mature egg is released from the ovary into the abdominal cavity. There it is captured by the funnel of the fallopian tube, in which it meets the sperm. After fertilization, the egg enters the uterine cavity, where the embryo begins to develop. But sometimes two eggs ripen at the same time, which can be fertilized. In this case, each embryo will develop independently inside its fetal bladder and will be associated with the mother's body by its own placenta. Such twins often do not even look alike, they can be of different sexes, they can have a different blood type. This is because each egg is completely unique. Such children are called fraternal twins. Identical twins are obtained by fertilizing one egg with a large nucleus and a double or even triple set of chromosomes. These abnormal eggs are called polyploid eggs. Likewise, male germ cells can also have a double set of chromosomes. Such sperm are also called polyploid. When a polyploid sperm and a polyploid egg are found, two embryos develop after fertilization. This type of twin is much less common. Identical twins are always of the same sex. They have the same appearance, a tendency to the same diseases. This similarity extends to the properties of the psyche, their characters are also often similar. Such twins feel their soul mate even from a distance. Often the fates of such people are the same. Many women dream of giving birth to twins. Most often this happens if the couple had cases of twins in the family. With in vitro fertilization, multiple pregnancies often develop. With age, the possibility of conceiving twins increases somewhat, especially if the woman has already had childbirth.
